1. Field of the Invention
The present invention relates to a spindle motor, a disk drive apparatus, and a method of manufacturing the spindle motor.
2. Description of the Related Art
Spindle motors arranged to rotate magnetic disks are usually installed in conventional hard disk drives. Such spindle motors include a stationary portion and a rotating portion. The stationary portion is fixed to a housing of the drive. The rotating portion is arranged to rotate while holding a magnetic disk. The spindle motor is arranged to generate a torque centered on a central axis through magnetic flux generated between the stationary portion and the rotating portion, so that the rotating portion is caused to rotate with respect to the stationary portion.
The stationary portion of the spindle motor includes coils arranged to generate the magnetic flux. End portions of conducting wires which define the coils are drawn out of the spindle motor, and soldered to a circuit board. For example, paragraph [0026] of JP-A 2009-110611 states that a copper wire portion of a coil wire is drawn out through a through hole, and soldered to a land portion of a flexible circuit board.
During a process of manufacturing a spindle motor, ultrasonic cleaning is typically performed after the above-described soldering to remove an extraneous material. However, if the spindle motor having the above-described structure is subjected to the ultrasonic cleaning, it may happen that stresses due to ultrasonic wave vibration are concentrated on a boundary region between the conducting wire and a solder. In order to prevent a break of the conducting wire from occurring due to this stress concentration, a known technique subjects the spindle motor to the cleaning with a reduced power of the ultrasonic wave vibration.
Regarding this problem, JP-A 2009-110611 describes a technique of arranging an outer circumference of a solder portion to have a diameter greater than that of a through hole of a base in order to prevent breakage of the coil wire. However, this technique is intended to improve rigidity of the solder portion and a small diameter portion of the flexible circuit board, and to thereby to reduce vibrations of these portions, as described in paragraph [0032] of JP-A 2009-110611. However, JP-A 2009-110611 does not mention a technique that prevents the above-described stress concentration.
Note that potential causes for the above-described stress concentration are not limited to the vibrations that occur at the time of the ultrasonic cleaning, but also include a variety of exterior shocks, such as, for example, vibrations that occur while the spindle motor is being carried or vibrations that occur while the spindle motor is being used.